Generation of electricity derived from structural response to the wind stream is a well-written story. The most familiar example is the windmill—a wind-driven propeller pointed into the wind by a trailing vane. This is the best-known representative of a class of rotary airfoils rotating around a horizontal axis. Among its many disadvantages are the need to keep it pointed into the wind, to provide for gearing, braking, and feathering controls to transfer the torque to an off-axis generator, and to keep the rotational speeds within acceptable limits.
Attempts have been made to provide for omni-directional response to the wind, that is, the ability to be driven without directional adjustment no matter what the direction of the wind is. With such a device, it is unnecessary to-point it into the wind because its axis of rotation is vertical.
The major problem with vertical axis rotors is that the wind blows on both sides of the axis of rotation, so that something must be done on a net basis to the baffles or airfoils on one side to resist the wind, and on the other side to pass the wind. Otherwise the rotor does not rotate because the force reaction is the same or nearly the same on both sides of the axis. Classical devices for this purpose include feathering of the foils or vanes on one side and supporting them on the other side.
This requires mechanism for the purpose, and generates considerable noise. Also the structure is not balanced, because it supports a much larger lateral load on one side than on the other.
The above problems were solved in an abandoned project a number of years ago. A number of wind turbines which included many of the features of this invention showed considerable promise, but were abandoned to the elements when the economic and environmental disadvantages of the systems were learned. For many years the advantages of this wind turbine would have been attainable if the rotor utilized in it and in this invention could successfully have been incorporated into in an acceptable total electrical generation system. The potentials of this wind turbine were neither appreciated, nor were the problems solved, so its potential benefits have remained unaccomplished.
Just as with a horizontal axis windmill, a conventional vertical axis wind turbine has heretofore required a gear box to transfer torque from the wind turbine's rotor turbine to the rotor of an electrical generator. While this appears to be a commonplace thing, these gear boxes are expensive, noisy, need maintenance, have speed limitations, and constitute a slow-speed drag which raises the lowest wind speed to which the system can respond and thereby forfeits the energy content of slow wind speed.
In addition to these disadvantages, gear boxes constitute a restraint on maximum speeds. An overspeed can lead to swift destruction of the mechanical system. To prevent this, either the wind responsive rotor has been at least partially disabled, or a braking system has been provided to limit its speed. A braking system conventionally feeds some of the generated power into a braking force. This seriously reduces the range of wind speeds from which energy can be extracted, and forfeits much energy that should be obtainable from high wind speeds.
It is an object of this invention to provide an elegantly simple wind turbine having an upright central axis, which turbine drives an electrical generator directly without intervening gearing or other transmission, and without the need to divert any of the wind-driven energy into velocity control over the turbine rotor itself. Then the wind turbine rotor can extract energy from a wind stream at any wind speed.
Further, it is an object of this invention to provide a rotationally stable and quiet system, without the vibration and noise which make windmill type systems poor neighbors. In fact, this system is so quiet that it can be installed in one's yard, where even a small system can readily generate useful amounts of electricity and at very slow wind speeds.
Yet another disadvantage of known tower-supported systems is their tendency to be toppled by high velocity winds. Very heavy supports are conventionally used to resist this tendency. This invention, by its use of a properly proportioned wind rotor utilizes the spatial rigidity of a rotating object to resist toppling movement, and enables an importantly stable installation. This stability is further enhanced by a lower profile dictated both by reduction of the height of a confronting aspect ratio, and by proportions that provide optimum spatial rigidity.